Ga doping to significantly improve the performance of all-electrochemically fabricated Cu2O–ZnO nanowire solar cells

Abstract

Cu₂O–ZnO nanowire solar cells have the advantages of light weight and high stability while possessing a large active material interface for potentially high power conversion efficiencies. In particular, electrochemically fabricated devices have attracted increasing attention due to their low-cost and simple fabrication process. However, most of them are “partially” electrochemically fabricated by vacuum deposition onto a preexisting ZnO layer. There are a few examples made via all-electrochemical deposition, but the power conversion efficiency (PCE) is too low (0.13%) for practical applications. Herein we use an all-electrochemical approach to directly deposit ZnO NWs onto FTO followed by electrochemical doping with Ga to produce a heterojunction solar cell. The Ga doping greatly improves light utilization while significantly suppressing charge recombination. A 2.5% molar ratio of Ga to ZnO delivers the best performance with a short circuit current density (J_sc) of 3.24 mA cm⁻² and a PCE of 0.25%, which is significantly higher than in the absence of Ga doping. Moreover, the use of electrochemically deposited ZnO powder-buffered Cu₂O from a mixed Cu²⁺–ZnO powder solution and oxygen plasma treatment could reduce the density of defect sites in the heterojunction interface to further increase J_sc and PCE to 4.86 mA cm⁻² and 0.34%, respectively, resulting in the highest power conversion efficiency among all-electrochemically fabricated Cu₂O–ZnO NW solar cells. This approach offers great potential for a low-cost solution-based process to mass-manufacture high-performance Cu₂O–ZnO NW solar cells.